Currently, the Milky Way and Andromeda galaxies are separated by about 2.3 million light-years and are moving toward each other at about 110 kilometers per second \((\mathrm{km} / \mathrm{s})\) Estimate how long it might take for the two to collide. Why do you think your answer may or may not be a good estimate of how long it will take these galaxies to fully merge?

The Milky Way is our home galaxy. It is a massive spiral galaxy, containing between 100 and 400 billion stars, along with planets, gas clouds, and dark matter.
The Milky Way’s size is immense, spanning about 100,000 light-years in diameter. We live in one of its spiral arms, known as the Orion Arm. At its center, there's a supermassive black hole called Sagittarius A*, which has a mass of about 4 million times that of our Sun.

The Milky Way is part of a group of galaxies called the Local Group. Its nearest large neighbor in this group is the Andromeda galaxy. Because both galaxies are so massive, they exert gravitational forces on each other, causing them to move towards an inevitable collision. This cosmic dance is a fascinating but slow process, unfolding over billions of years.

The Andromeda galaxy is a massive spiral galaxy similar to the Milky Way. It’s located approximately 2.3 million light-years from us. Andromeda is actually the closest spiral galaxy to the Milky Way and is the largest galaxy in the Local Group.

With an estimated one trillion stars, Andromeda is more than twice the size of the Milky Way. It is named after the constellation Andromeda, where it appears in the sky. Despite being so far away, it can be seen with the naked eye from Earth under dark skies.

Andromeda and the Milky Way are set on a collision course. Over billions of years, these two spiral galaxies will merge to form a new galaxy. This galaxy collision won't be a destructive event for individual stars due to the vast distances between them. However, the gravitational interactions will significantly alter the galaxies' structures.

Relative velocity is the speed at which two objects are moving towards or away from each other. In the case of the Milky Way and Andromeda galaxies, their relative velocity is about 110 kilometers per second (km/s).

Understanding relative velocity is crucial for estimating when the two galaxies will collide. Despite moving at extremely high speeds, the vast distance between them means the collision will take billions of years. The relative velocity can be determined by observing the Doppler shift of the light from Andromeda.

However, while we use the current relative velocity for simple calculations, it's important to remember this speed is not constant. Gravitational forces between the galaxies and other cosmic objects can cause changes in their velocities, making precise predictions challenging.

Light-years are a measure of distance that astronomers use to describe how far light travels in one year. One light-year equals approximately 9.461 trillion kilometers (or specifically, 9.461 x 10^12 km).

For the Milky Way and Andromeda collision estimation, we start with a distance of 2.3 million light-years. To convert this to kilometers, we multiply by the number of kilometers in one light-year:
2.3 million light-years x 9.461 x 10^12 km/light-year = 2.17603 x 10^19 km.

This conversion is essential for calculating the time it will take for the galaxies to collide when we know their relative velocity in kilometers per second. By changing the light-year distance into kilometers, we can apply straightforward mathematical formulas to estimate the time until collision.